1. Field of the Invention
The present invention relates to a curved suction box apparatus for guiding a web towards a nip defined by a pair of cooperating rolls or a nip of an extended nip press.
More particularly, the present invention relates to a curved suction box apparatus which avoids the need for suction rolls or the like.
2. Information Disclosure Statement
In a press section of a papermaking machine, a suction pick-up roll is usually provided for transferring a formed web from a fourdrinier wire onto a press felt such that the press felt guides the formed web towards a downstream pressing nip.
Also, when the formed web is supported beneath the aforementioned press felt for guidance towards a nip press, the web is preferably subjected to a flow of steam prior to passage of the formed web through the nip.
More particularly, the steam is usually applied directly to the surface of the web by means of a steam box or the like. A vacuum box is disposed on the opposite side of the web for extracting excess steam from the web.
More specifically, when heat is applied to a formed web supported on a press felt such as by the application thereto of steam, the viscosity and surface tension of the water within the web is reduced and the fibers within the web are softened and are hence easier to compact, due to the increased temperature thereof. Such decreased viscosity and fiber softening facilitates removal of additional quantities of water from the web while strengthening the web during subsequent pressing of the web through the nip press.
However, the provision of a suction pick-up roll or the provision of one or more vacuum rolls in the vicinity of the steam box involves considerable expense during manufacture thereof. For example, a suction roll may require 600 man hours for drilling the roll shell thereof. Also, such roll requires the provision of relatively complex internal sealing glands and the like. Therefore, it is not unusual for a suction roll to cost $1 million or more.
The present invention overcomes the aforementioned costly procedures by the provision of an integrated suction box which includes an initial shoe having a convex surface and a further shoe defining a further convex surface with a suction box disposed between the respective shoes.
Alternatively, the present invention includes an arrangement including a suction box and only one shoe.
The aforementioned curved suction box apparatus enables removal of the web from a fourdrinier forming wire onto a press felt or, alternatively, enables guidance of a web while such web is subjected to saturation with steam.
Therefore, it is a primary objective of the present invention to provide a curved suction box apparatus which overcomes the aforementioned inadequacies of the prior art proposals and which makes a considerable contribution to the art of guiding a web in a press section.
Another object of the present invention is the provision of a curved suction box apparatus which includes an initial shoe which defines a convex surface for guiding the web, a box disposed downstream relative to the initial shoe and a further shoe which defines a further convex surface for guiding the web from the box towards a nip press.
Another object of the present invention is the provision of a curved suction box apparatus in which the initial and further shoe are of ceramic material in order to reduce wear thereof.
Another object of the present invention is the provision of a curved suction box apparatus in which the convex and further convex surfaces of the shoes define a plurality of perforations connected to a source of partial vacuum for drawing the web towards the respective convex surfaces.
A further object of the present invention is the provision of a curved suction box apparatus in which the box includes a first and a second compartment so that the rate of removal of steam from the web can be regulated in a machine direction.
Another object of the present invention is the provision of a curved suction box apparatus which includes a plurality of showers for supplying lubricating water to the respective surfaces of the curved suction box apparatus for reducing frictional wear between such surfaces and the web or a press felt supporting the web.
Other objects and advantages of the present invention will be readily apparent to those skilled in the art by a consideration of the detailed description contained hereinafter, taken in conjunction with the annexed drawings.